Microcapsules and microencapsulation technology are old and well known and their commercial applications varied. Microcapsules have played a significant role in various print technologies where a paper or other like substrate is coated with microcapsules containing ink or an ink-forming or inducing ingredient which microcapsules release the ingredient, generating an image, when fractured by pressure, as by a printing press or a stylus. Microcapsules have also played a significant role in various adhesive and sealant technologies including the encapsulation of solvents for solvent swellable/tackified preapplied adhesives whereby fracture of the microcapsules releases the solvent which softens or tackifies the adhesive to enable bonding and which re-hardened upon evaporation of the solvent. In other adhesive and sealant applications, the microcapsules contain one or more components of a curable or polymerizable adhesive or sealant composition which, upon release, leads to the cure or polymerization of the adhesive or sealant. In all of these early applications, functionality and efficacy, especially for long term storage and utility, is dependent upon the integrity of the microcapsule walls where the sought after integrity pertains to both strength, so as to avoid premature fracture, as well as impermeability, so as to prevent leakage and/or passage of the contents of the microcapsule through the microcapsule walls. In the former situation, parts having a preapplied microencapsulated adhesive have a tendency to bond together if they hit one another or are stacked upon one another where the pressure of the stack is sufficiently high. Even if not bonded, the fracture of the microcapsules results in less adhesive to effect the bond when the bond is intended. Similarly, if the microcapsule walls allow permeation of the active components through the cell wall, even a slow permeation, the product is short lived as cure will be effected when not intended.
As with most any technology, evolution of microencapsulation technology has led to many new applications, including applications that require changes in the physical properties of the microcapsules, especially their walls. New applications require microcapsules that fracture more readily, with less pressure, but not prematurely. Other applications require microcapsules that specifically allow for a controlled, slow release or permeation of the contents from within the microcapsules without the need to actually fracture the same. For example, perfume containing microcapsules are oftentimes applied to advertising inserts in magazines so that the reader can sample the smell of the perfume. Here strength is needed to avoid premature fracturing of the microcapsules due to the weight and handling of the magazine; yet, the microcapsules need ease of fracture so that the reader can simply scratch the treated area to release the contents of the microcapsule. At the same time, it is desirable to allow for some release of the contents, even without fracturing, to induce the reader to want to scratch the sample to get a more accurate sense of the smell.
Another application for microcapsules is in laundering and fabric treatments. A number of products exist wherein microcapsules of various ingredients, including perfumes, are applied to strips of a fabric material and added to the dryer wherein the tumbling action and/or heat of the dryer causes the microcapsules to fracture, releasing the ingredients which, in a volatilized state, permeate and deposit upon the contents of the dryer. This methodology applies that “fresh out of the dryer” smell, but is short lived as the perfume continues to volatilize from the treated fabric. Other products exist whereby microcapsules containing perfumes and other ingredients are applied directly or indirectly to the fabric, especially apparel, to provide a longer lived freshness to the same. Here, the performance or efficacy of these products is oftentimes short lived as the content of the microcapsules escapes too readily from the microcapsules and/or the walls of the microcapsules are too weak and/or have too little give such that normal wearing of the fabric causes the microcapsules to break too readily. Opportunities abound for new microcapsules that address the specific requirements of a given application as well as microcapsules that offer better performance and properties than are attainable with current state of the art microcapsule technology.
Whether applications have driven the evolution of microcapsule technology or the evolution of microcapsule technology has driven their expanded applications, or perhaps a little of both, there has been and continues to be constant development in microencapsulation technology, both in terms of their production/process methodology and their chemistry. Early melamine formaldehyde microcapsules continue to evolve; yet concurrently, they have, to some extent, given way to acrylic and other microcapsule chemistries and technologies. In turn, both have continued to evolve further to dual walled microcapsules of each chemistry as well as both chemistries. While the basic building blocks of the capsule walls have largely remained the same, the specific selection of building blocks and methodology has led to newer and improved microcapsules enabling the microencapsulation of a broader array of ingredients, compounds and elements.
Despite all the advances and improvements, there is still a need for improved specialty microcapsules that provide a suitable mix of release/permeability characteristics and physical properties for today's demanding applications. This is especially so in the area of perfumes and other odiferous ingredients, particularly in relation to fabric, textile and garment treatment, where controlled release and longevity as well as capsule strength and integrity are necessary.